1. Field of Invention
This invention is generally directed to imaging members for electrophotography. More specifically, this invention is directed to a multilayer imaging photoreceptor having a mechanically and electrically robust undercoating layer.
2. Description of Related Art
In electrophotography, an electrophotographic imaging member, also commonly referred to as a photoreceptor, containing a photoconductive layer on a conductive layer, is imaged by first uniformly electrostatically charging the surface. The substrate is then exposed to a pattern of activating electromagnetic radiation, such as light. The light or other electromagnetic radiation selectively dissipates the charge in the illuminated areas of the photoconductive insulating layer while leaving behind an electrostatic latent image in the non-illuminated areas. This electrostatic latent image may then be developed to form a visible image by depositing finely divided electrostatically charged marking particles, generally referred to as toner particles, on the surface of the photoconductive layer. The resulting visible image may then be transferred from the electrophotographic imaging member to a support such as paper. This image developing is repeated as many times as necessary with reusable photoconductive layers.
An electrophotographic imaging member may take one of many different forms. For example, layered photoresponsive imaging members are known in the art. U.S. Pat. No. 4,265,990, which is incorporated herein by reference in its entirety, describes an exemplary layered photoreceptor having separate photogenerating and charge transport layers. The photogenerating layer is capable of photogenerating holes and injecting the photogenerated holes into the charge transport layer.
More advanced photoreceptors contain highly specialized component layers. For example, a multilayered photoreceptor that can be employed in electrophotographic imaging systems can include a substrate, a charge blocking undercoating layer, a charge generating layer (including photogenerating material in a binder) over the undercoating layer, and a charge transport layer (including charge transport material in a binder). Additional layers such as an overcoating layer or layers can also be included.
The photoconductors currently used are susceptible to carrier injection from the substrate into the photosensitive layer such that the charge on the surface of the photoconductor may be microscopically dissipated or decayed. This can result in production of a defective image. The interposition of an undercoating layer between the substrate and the photosensitive layer has been suggested to overcome this problem, and improve the chargeability of the photoconductor and enhance adhering and coating properties of the photosensitive layer with respect to the substrate.
U.S. Pat. No. 5,958,638, which is incorporated herein by reference in its entirety, discloses known materials used for undercoat layers. For example, such materials have included a resin material alone, such as polyethylene, polypropylene, polystyrene, acrylic resin, vinyl chloride resin, vinyl acetate resin, polyurethane, epoxy resin, polyester, melamine resin, silicone resin, polyvinyl butyryl, polyamide and copolymers containing two or more of repeated units of these resins. The resin materials further have included casein, gelatin, polyvinyl alcohol, ethyl cellulose, etc.
The undercoat layers are typically formed by a dip coating method. See, for example, U.S. Pat. No. 5,958,638 and U.S. Pat. No. 5,891,594.
In photoreceptors of the above type, the photogenerating material generates electrons and holes when subjected to light. In the case of a hole blocking undercoating layer, the undercoating layer prevents holes in the conductive ground plane from passing into the photogenerator from which they would be conducted to the photoreceptor surface, thus dissipating the surface charge of the photoconductor. The undercoating layer does permit electrons generated in the photogenerator to pass to the conductive ground plane, preventing an undesirably high electric field from building up across the generator upon repeated usage or cycling of the photoconductive imaging member.